<template>
  <ul class="list">
      <li
         class="item"
         v-for="item of letters"
         :key="item"
         ref="item"
         @touchstart="handleTouchStart"
         @touchmove="handleTouchMove"
         @touchend="handleTouchEnd"
         @click="handleLetterClick"
         >
       {{ item }}
     </li>
  </ul>
</template>

<script>
 export default {
    name: 'Alphabet',
    props: {
       cities: Object
    },
    computed: {
      letters () {
        const letters = []
        for(let i in this.cities){
           letters.push(i)
        }
        return letters
      }
    },
    data () {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    updated () {
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
       handleLetterClick (e) {
          this.$emit('change',e.target.innerText)
       },
       handleTouchStart () {
          this.touchStatus = true
       },
       handleTouchMove (e) {
          if (this.touchStatus) {
            if(timer){
              clearTimeout(this.timer)
            }
            this.timer = setTimeout(() => {
                const touchY = e.touches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
                if(index >= 0 && index < this.letters.length){
                   this.$emit('change',this.letters[index])
                }
            },16)
          }
       },
       handleTouchEnd () {
          this.touchStatus = false
       }
    }
 }
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
     display: flex
     flex-direction: column
     justify-content: center
     position: absolute
     top: 1.58rem
     right: 0
     bottom: 0
     width: .4rem
     .item
         line-height: .4rem
         text-align: center
         color: $bgColor

</style>
